a) Field of the Invention
The present invention is directed to the detection and imaging of the internal geometry of the eye, particularly of the important components for imaging in the eye such as the cornea, lens, vitreous body and retinal surface, by means of multiplex multichannel short coherence interferometry.
b) Description of the Related Art
Owing to new developments in ophthalmology characterized by many different types of operative procedures on the eye lens (e.g., cataract surgery) and on the cornea (refractive cornea surgery), there is a considerable demand for measurement methods which show the optically active geometry of the eye quantitatively. One task in this connection is the measurement of the imaging quality of the eye. Various methods for detecting the imaging quality of the eye are already known: subjective methods requiring the cooperation of the test subject and objective methods which dispense with the cooperation of the test subject in the measurement in the stricter sense. Subjective methods are rarely used due to the required cooperation of the test subject for rigorous clarification of clinical questions. Also, the previously known objective methods for detecting aberrations in the eye allow only limited access to the geometric structure of the eye because they only show the total effect of all optically active structures of the eye and can not clearly separate the influences of individual components. A recent overview of these questions and a comparison of two modem subjective methods for measuring the aberrations of the eye are found, for example, in E. Moreno-Barriuso, R. Navarro, J. Opt. Soc. Am. A, Vol. 17 (2000): 974-985.
Short coherence interferometry offers an objective method for the quantitative detection of the optically active geometry of the eye. In this method, interferometric measurement beams of a two-beam interferometer are directed to the object and penetrate into the depth of the latter. The depth positions of light-reemitting locations are measured along these measurement light beams approximately in the direction of the visual axis or optic axis of the eye. When measuring by means of these depth scans, as they are called, the length of the reference beam is continuously changed, e.g., by axial displacement of the reference mirror, and the short coherence interferogram is accordingly registered along the depth coordinate of the measurement beam in the measurement object. When the length of the reference beam within the coherence length, that is, within the so-called coherence window, matches the length of the measurement beam to a light-reemitting structure, interference occurs at the interferometer output. This interference generates an electric AC signal at the photoelectric detector at the interferometer output, which AC signal represents the light-reemitting structure. The instantaneous length of the reference beam gives the associated depth position of this light-reemitting location in the measurement beam. In order to ensure a meaningful transverse resolution, the measurement beam is focused on the object structure under consideration or a dynamic focus is used which scans the object depth in longitudinal direction synchronously with the coherence window. The electric signal of the photoelectric detector at the interferometer output then contains the depth structure along the measurement beam. The topography of the intraocular structures can then be determined from depth scans of the kind mentioned above which are carried out through transversely adjacent pupil points of the eye; tomographic images can also be synthesized from an appropriate quantity of these transversely adjacent depth scans. These methods are known as optical coherence tomography and optical coherence topography and are described in A. F. Fercher and C. K. Hitzenberger, Springer Series in Optical Sciences (ed. T. Asakura), Vol. 4, Springer Verlag, Berlin 1999.
The described short coherence interferometry has the disadvantage that many individual transversely adjacent depth scans must be carried out along individual measurement beams one after the other in a time-consuming manner to obtain topograms or tomograms. In particular, the use of a method of this type on patients is problematic.